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Molecular effects on mean excitation energies
Author(s) -
Peek James M.
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560360855
Subject(s) - excitation , excited state , atomic physics , sum rule in quantum mechanics , dipole , wave function , chemistry , additive function , atom (system on chip) , electron , physics , quantum mechanics , mathematics , mathematical analysis , computer science , embedded system , quantum chromodynamics
Approximate wave functions are used to evaluate the excitation energy moments of dipole oscillator strength sums for molecules containing hydrogen. For moments that have sum‐rule expressions requiring only the initial‐state wave function, these expectation values consist of terms having the appearance of the additivity of constituent atom quantities or Bragg–Kleeman approximation plus, possibly, two‐electron terms. These atomic‐like terms differ from those used in the Bragg–Kleeman approximation by containing parameters representative of the molecular bonding and by showing a dependence on the initial vibrational state. Effects due to rotation are limited to the smaller two‐electron terms. A suppression of the rotation–vibration effects is indicated since some moments do not contain two‐electron terms and if the initial vibrational state is not too highly excited. A simple method for determining the bonding parameters is suggested and a formal relationship then provides predictions for the mean excitation energies with knowledge of just the molecular sum‐rule data and available atomic data. Numerical data for H 2 , H 2 O, and NH 3 targets are presented which are in reasonable agreement with experiment or best available estimates.